Ammonia is the principal nitrogenous waste product of teleosts and many invertebrates in both freshwater and seawater. The ammonia results from the deamination or transamination of proteins the organism receives via its diet. However, high ammonia concentrations can be toxic to many of these same aquatic organisms. In natural systems, such as lakes, rivers and oceans, the concentration of ammonia rarely reaches deleterious levels because the density of fish (and other organisms) per mass of water is low.
However, in man-made aquatic systems such as aquaculture rearing pens, tanks, raceways and ponds plus aquaria, both public and private, ammonia can reach toxic concentrations, sometimes very quickly. One reason for this is that in the above-named systems the fish density can be very large in relation to the small amount of water. Another reason is that in many of these systems the water is not continually changed; rather it recirculates through the system with only periodic partial water changes.
Therefore, most aquaculture systems and aquaria use filtration, in one form or another, to maintain a degree of water quality that is suitable for the maintenance and growth of aquatic organisms. A major component of any such filtration unit is the biological filter. The biological filter gets its name from the fact that it acts as a substrate or site for the growth of bacteria which have the capability to convert, by way of oxidation, ammonia to another compound—nitrite. High concentrations of nitrite can also be toxic but there are other species of bacteria which grow on the biological filter and oxidize the nitrite to nitrate, such as those described in U.S. Pat. Nos. 6,268,154, 6,265,206 and 6,207,440, each of which is incorporated by reference herein in its entirety as if fully set forth. Nitrate is considered non-toxic to aquatic organisms except in extreme cases of very high concentrations.
There are other situations or applications which use biological filters. These include sewage treatment facilities, wastewater treatment facilities and drinking water filtration plants. While each will have its own particular reason for using a biological filter, the goal is the same: the conversion of toxic inorganic nitrogen compounds to less harmful inorganic nitrogen substances. Biological filtration is necessary for many facilities to meet the National Recommended Water Quality Criteria as set by the Environmental Protection Agency (EPA) of the United States of America.
The oxidation of ammonia to nitrite is a bacterially-mediated process. Specifically, it is a two step oxidation process involving the conversion of ammonia to nitrite according to the following equations:NH3+O2+H2O+2e−--->NH2OH+H2O  (1)NH2OH+H2O--->NO2−+5H++4e−  (2)
The most commonly studied ammonia oxidizing bacteria (AOB) is Nitrosomonas europaea. It was originally isolated from soils and is purported to be the active AOB in aquaculture facilities (Wheaton, F. W. 1977. Aquacultural Engineering. John Wiley & Sons, Inc. New York.), in wastewater treatment facilities (Painter, H. A. 1986. Nitrification in the treatment of sewage and waste-waters. In Nitrification J. I. Prosser ed. IRL Press. Oxford.) and in aquaria (Spotte, S. 1979. Seawater Aquariums—The Captive Environment. Wiley-Interscience. New York). These references, and all other references cited herein are hereby incorporated by reference in their entirety as if fully set forth.
However, recent research conducted with modem molecular methods which use the uniqueness of the DNA sequence of an organism (or group of organisms) has shown that N. europaea and its close relatives were below detection limits in freshwater aquaria environments (Hovanec, T. A. and E. F. DeLong. 1996. Comparative analysis of nitrifying bacteria associated with freshwater and marine aquaria. Appl. Environ. Microbiol. 62:2888-2896.). Other research has demonstrated that N. europaea is not the dominant AOB in wastewater treatment facilities (Juretschko, S. et. al. 1998. Combined molecular and conventional analyses of nitrifying bacterium diversity in activated sludge: Nitrosococcus mobilis and Nitrospira-like bacteria as dominant populations. Appl. Environ. Microbiol. 64:3042-3051).
Moreover, an environmental factor of particular import with aquaria environments and wastewater treatment is salinity, and, more specifically, the numerous physicochemical differences between freshwater and saltwater environments. The distinction among various AOBs in their ability to tolerate such dramatic changes in local environment is critical in the design of these systems and implementation of AOBs therein. As such, a demonstrated tolerance by a particular AOB to a saltwater environment may render that AOB suitable for use in particular aquaria and wastewater environments, and, moreover, a resilience to withstand the change between a freshwater and saltwater environment may have even broader implications.
Furthermore, the storage and transport of AOB is often limited to liquid and similar, potentially inconvenient media, owing, at least in part, to the inability of various strains of AOB to withstand a freeze-drying process. Such a process allows one to formulate a volume of AOB into a solid, freeze-dried powder or similar composition that may be tolerant of greater fluctuations in, e.g., temperature, and may be correspondingly more practical for purposes of shipping and handling in a commercialized product, or similar considerations, and for maintaining an extended shelf-life.
Thus, there exists a need in the art for the identification of AOBs, particularly those which are capable of tolerating a saltwater environment and/or both saltwater and freshwater environments. There is also a need in the art for AOBs that remain viable after being subjected to a freeze-drying process.